title: Cytochrome b₅ reductase-cytochrome b₅ as an active P450 redox enzyme system in Phanerochaete chrysosporium: atypical properties and in vivo evidence of electron transfer capability to CYP63A2.
abstract: Two central redox enzyme systems exist to reduce eukaryotic P450 enzymes, the P450 oxidoreductase (POR) and the cyt b₅ reductase-cyt b₅. In fungi, limited information is available for the cyt b(5) reductase-cyt b(5) system. Here we characterized the kinetic mechanism of (cyt b₅r)-cyt b₅ redox system from the model white-rot fungus Phanerochaete chrysosporium (Pc) and made a quantitative comparison to the POR system. We determined that Pc-cyt b₅r followed a "ping-pong" mechanism and could directly reduce cytochrome c. However, unlike other cyt b₅ reductases, Pc-cyt b₅r lacked the typical ferricyanide reduction activity, a standard for cyt b₅ reductases. Through co-expression in yeast, we demonstrated that the Pc-cyt b₅r-cyt b₅ complex is capable of transferring electrons to Pc-P450 CYP63A2 for its benzo(a)pyrene monooxygenation activity and that the efficiency was comparable to POR. In fact, both redox systems supported oxidation of an estimated one-third of the added benzo(a)pyrene amount. To our knowledge, this is the first report to indicate that the cyt b₅r-cyt b₅ complex of fungi is capable of transferring electrons to a P450 monooxygenase. Furthermore, this is the first eukaryotic quantitative comparison of the two P450 redox enzyme systems (POR and cyt b₅r-cyt b₅) in terms of supporting a P450 monooxygenase activity.
authors.affiliation: Environmental Genetics and Molecular Toxicology Division, Department of Environmental Health, University of Cincinnati College of Medicine, Cincinnati, OH 45267-0056, USA.
authors.forename: Khajamohiddin
authors.initials: K
authors.lastname: Syed
authors.forename: Chandramohan
authors.initials: C
authors.lastname: Kattamuri
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Thompson
authors.forename: Jagjit S
authors.initials: JS
authors.lastname: Yadav
mesh_terms: D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D042966:Cytochrome-B(5) Reductase / Q000235:genetics / Q000378:metabolism*; D015786:Cytochromes b5 / Q000235:genetics / Q000378:metabolism*; D004579:Electron Transport; D004926:Escherichia coli / Q000235:genetics; D015870:Gene Expression; D010084:Oxidation-Reduction; D020075:Phanerochaete / Q000201:enzymology* / Q000235:genetics; D010843:Pichia / Q000235:genetics; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D011994:Recombinant Proteins; D015786:Cytochromes b5; D003577:Cytochrome P-450 Enzyme System; D042966:Cytochrome-B(5) Reductase